In modern deployment of network gateways (of different kinds, especially PGW/SGW in 3GPP architecture) it is extremely important to provide high availability, as any downtime is disastrous. An example of a network where high availability is important is a 3rd Generation Partnership Project (3GPP) long term evolution (LTE) network including an evolved packet core (EPC). The EPC includes multiple network gateways including serving gateways (SGWs) and packet data network (PDN) gateways (PGWs). Both of these types of gateways require high availability for the proper function of the EPC.
In many networks, multiple physical chassis are deployed to work as a single logical entity that implements multiple network gateways or other components of a network. A chassis is a physical housing for networking devices that may be modular to include add on components. Such a configuration using multiple chassis is known as Inter Chassis Redundancy (ICR), where failure of one chassis results in transferring its loads (e.g. user sessions) to another chassis. Inter chassis resilience provides session resilience support across multiple nodes (typically two nodes) in different regions to allow geographical redundancy. ICR is intended to provide node level session resilience functionalities using a 1:1 redundancy model with two nodes. One node acts as active node which handles live sessions and user traffic and the other node acts as hot standby to back up the active node.
Network redundancy in an EPC can be based on the S1-Flex mechanism. The S1-Flex mechanism provides support for network redundancy and load sharing of traffic across network elements in the EPC. The components of the EPC including the mobility management entity (MME) and SGW can have redundancy by creating a pool of MMEs and SGWs and allowing each eNodeB (an evolved node B that connects the EPC to a radio access network (RAN)) to be connected to multiple MMEs and SGWs in a pool. The S1-Flex mechanism ensures functionality and flexibility with no single point of failure thereby providing a high availability for the EPC to the user equipment attached to the RANs.